Project Summary Mono/macrophagic commitment of myeloid cells comprises two distinct and largely independent developmental steps. First, hematopoietic stem cells asymmetrically divide to generate a succession of lineage-restricted progenitors that culminate in differentiation of peripheral, post-mitotic monocytes. Second, blood-circulating monocytes are short-lived cells that can undergo differentiation into macrophages, which are specialized phagocytic cells capable of infiltrating most tissues. While monocytes can mediate inflammation and cell toxicity, to some extent, macrophages boast the widest set of defense mechanisms against pathogens and can elicit a robust inflammatory response. In this proposal, we analyze the molecular determinants of monocytic and macrophagic development by profiling the zinc-finger EGR1 transcription factor that has been previously implicated in myeloid cell development. EGR1 is essential for development of monocytes and binds a set of critical enhancers that regulate monocytic differentiation. In macrophages, however, EGR1 boasts an additional repressor function at inflammatory enhancer elements. We propose to dissect the scope of action of EGR1 in macrophages and identify the protein partners that cooperate with EGR1 to regulate the epigenome. Furthermore, we propose to elucidate the chromosome conformation changes that accompany late-stage development of myeloid cells and determine how they impact a macrophage?s ability of promoting inflammation.